Addition of probiotic to a feedlot diet alters the upper respiratory tract microbiome in feedlot steers

Authors: McDaneld, Tara; Chitko-Mckown, Carol; Kuehn, Larry; BRYAN, KEITH - Novonesis

Submitted to: Conference Research Workers Disease Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 11/25/2025
Publication Date: 1/21/2026
Citation: McDaneld, T.G., Chitko-McKown, C.G., Kuehn, L.A., Bryan, K.A. 2026. Addition of probiotic to a feedlot diet alters the upper respiratory tract microbiome in feedlot steers [abstract]. In proceedings: Conference of Research Workers in Animal Diseases, Chicaog, IL. January 17-20, 2026. p. 347.

Interpretive Summary: Bovine respiratory disease (BRD) remains a serious health and economic problem for cattle producers and is often caused by a combination of bacterial and viral infections. To imitate BRD pathogens without introducing any into the herd, animals were administered lipopolysaccharide (LPS). By using LPS, we hope to reproduce the inflammatory response mounted by cattle when they become infected with a complex of bacterial and viral pathogens. In addition, probiotics are a promising intervention for modulating the bacterial populations and the immune system, promoting health benefits in cattle. By adding a commercial probiotic to the feedlot diet, we wanted to determine if it impacted the bacterial populations of the upper respiratory tract. At weaning into the feedlot environment, nasal swabs were collected from 360 steers (12 pens of 30 steers each). Shortly after weaning, steers were fed a traditional post-weaning diet with a commercial probiotic (6 pens of 30 calves each) or without a commercial probiotic (6 pens of 30 calves each). Approximately 4 weeks after weaning, steers were administered LPS or a saline control. Nasal swabs were collected at the day of administration of LPS or saline (Day0) and day 2 after administration of LPS or saline (Day2). DNA was exacted from the nostril swabs and the bacterial populations were identifed. Overall, diversity of the bacterial populations decreased at Day0 and Day2 compared to when the steers were weaned at the feedlot 4 weeks earlier. Addition of the probiotic also altered the abundance of the bacterial agents of the upper respiratory tract at Day0 and Day2. In conclusion, these findings contribute to the understanding of the dynamic nature of bacterial diversity and the potential effects of probiotics within the bovine respiratory tract and provides insight for future studies of probiotics on animal health, disease prevention, and management.

Technical Abstract: Bovine respiratory disease (BRO) remains a serious health and economic problem for cattle producers and is often caused by a combination of bacterial and viral infections. To imitate BRO pathogens without introducing any into the herd, animals were administered lipopolysaccharide (LPS). By using LPS, we hope to reproduce the inflammatory response mounted by cattle when they become infected with a gram-negative bacterial pathogen. In addition, probi-otics are a promising intervention for modulating the microbiome and the immune system, promoting health benefits in cattle. By adding a commercial probiotic to the feedlot diet, we wanted to determine if it impacted the microbiome. At weaning into the feedlot environment, nasal swabs were collected from 360 steers (12 pens of 30 steers each). Shortly after weaning, steers were fed a traditional postweaning diet with a commercial probiotic (50 mg/head daily, BOVAMINE Defend® Novonesis; 6 pens of 30 calves each) or without a commercial probiotic (6 pens of 30 calves each). Approximately 4 weeks after weaning, steers were administered LPS (0.5 µg/kg; in 1-3 ml of saline) or a saline control subcutaneous. Nasal swabs were collected at weaning and ai the day of administration of LPS or saline (Day0) and d 2 after administration of LPS or saline (Day2). DNA was exacted from the nostril swabs and 16S ribosomal RNA gene hypervariable regions 1-3 were subsequently sequenced. Overall, diversity of the microbiome decreased at Day0 and Day2 compared with when the steers were weaned at the feedlot 4 weeks earlier, and the bacterial profiles changed from weaning to Day0 and Day2. Addition of the probiotic also altered the microbiome of the upper respiratory tract at Day0 and Day2, including a change in abundance of Mycoplasma. In conclusion, these findings contribute to the understanding of the dynamic nature of bacterial diversity and the potential effects of fed probiotics within the bovine respiratory tract and provide insight for future studies of probiotics on animal health, disease prevention, and management.